Embodiments of the present disclosure relate to fuel vapor processing apparatus that may include a canister for adsorbing fuel vapor generated in a fuel tank, and a closing valve provided in a vapor passage connecting the canister and the fuel tank to each other.
JP-A-2011-256778 discloses a fuel vapor processing apparatus that may include a closing valve (control valve) provided in a vapor passage connecting a canister and a fuel tank to each other. The closing valve may include a non-sensitive range (valve closing range) for closing the valve, and a communicating range (valve opening range) for allowing flow of fuel vapor through the closing valve. When the closing valve is in the valve closing range, the fuel tank may be kept at a closed state. On the other hand, when the closing valve is in the valve opening range, fuel vapor produced in the fuel tank may be released toward the canister, so that the internal pressure of the fuel tank may be reduced.
The fuel vapor processing apparatus of the above document is configured to perform a learning control in which the degree of opening of the closing valve is changed in an opening direction from a fully closed position at a fixed speed. The degree of opening of the closing valve given at the time when the internal pressure of the fuel tank begins to be reduced may be stored as a valve open start position.
In order to learn the valve open start position of the closing valve with high accuracy, it may be necessary to change the opening degree of the closing valve in the opening direction at a relatively low speed. However, according to the learning control of the above document, the opening degree of the closing valve may be changed at the fixed speed or a constant speed. As a result, it may take a relatively long time for accurately perform the learning control.
Therefore, there has been a need in the art for enabling a learning control to be accurately performed in a relatively short time.